Allopolyploid Brassica juncea is particularly enriched in sinigrin, a kind of 3C aliphatic glucosinolates (GSLs), giving rise to characteristic taste after picking. However, the molecular mechanism underlying 3C aliphatic GSLs biosynthesis in this species remains unknown. In this study, we genome-widely identified GSLs metabolic genes, indicating different evolutionary rate of GSLs metabolic genes between subgenomes of B. juncea. Eight methythioalkylmalate synthase (MAMs) homologs were identified from B. juncea, in which six MAM1s were located in chloroplast and the other two were not detected with any expression. Furthermore, BjMAM1-4, BjMAM1-5, and BjMAM1-6 displayed higher expression levels in leaves than other tissues. Silenced expression analysis revealed that BjMAM1-4 and BjMAM1-6 function in 3C and 4C aliphatic GSLs accumulation. The specificity of the substrate selection for the second cycle reaction is much lower than that of the first cycle, suggesting these genes may preferentially catalyze 3C aliphatic GSLs biosynthesis. Our study provides insights into the molecular mechanism underlying the accumulation of 3C aliphatic GSLs, thereby facilitating the manipulation of aliphatic GSLs content in B. juncea.

Viruses are representative of a global threat to agricultural production. Genetic resistance is the preferred strategy for the control of viral infection and against loss of crop yield. Viral protein synthesis requires host cellular factors for translating their viral RNAs, and for regulating their replication and cell to cell systemic movement. Therefore, the viruses are dependent on cellular translation factors. Mutations in the gene encoding eIF4E and eIF4G or their isoforms, eIFiso4E, eIFiso4G and eIF2Bβ have been mapped as a source of plant potyvirus while other genus of plant virus recessive resistance genes in many species are originated from these loci. Some of other plant translation factors, such as eIF3, eIF4A-like helicases, eEF1A and eEF1B, which are required in interacting with viral RNAs and regulating various aspects of the infection cycle, have also been identified. Here, we summarized the mechanisms utilized by RNA viruses of eukaryotic plants and the essential roles of eIFs in virus infection. Moreover, we discussed the potential of eIFs as a target gene in the development of genetic resistance to viruses for crop improvement. This review highlighted newly revealed examples of abnormal translational strategies and provided insights into natural host resistance mechanisms that have been linked to 3′ cap-independent translational enhancer activity.

Brassica juncea is an allopolyploid originating from the interspecific hybridization between Brassica rapa and Brassica nigra, which is of multiple usage as a vegetable, oilseed and condiment worldwide. Both vernalization and non-vernalization under long-day photoperiod can promote floral transition in B. juncea suggesting merged flowering pathways of its ancestors and better environmental adaptability. We identified genome-wide flowering regulatory genes in B. juncea, which include 84 and 79 genes from A and B sub-genomes, respectively. Ka/Ks analysis revealed a purification effect on both photoperiod and vernalization flowering regulation pathways during evolution. Expression profile of those genes during long-day and vernalization treatments suggested BjuACO4, BjuAFT1, BjuBFT4, BjuASOC1 and BjuASOC4 may be the major functional copies of B. juncea flowering regulation. Further functional studies about BjuCOs showed three days delayed flowering time in BjuACO4 or BjuBCO3 silenced plants. Increased transcription of all BjuFLCs in BjuACO4 or BjuBCO3 silenced plants suggested interactions between photoperiod and vernalization pathways governing flowering time. Our findings provided flowering regulating networks in allopolyploid B. juncea.